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<TITLE>The list Data Abstraction</TITLE>
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<H2>6.1 The list Data Abstraction</H2>
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<P>The <B><I><A HREF="../stdlibref/vector.html">vector</A></I></B> data structure is a container of relatively fixed size. While the Standard C++ Library provides facilities for dynamically changing the size of a vector, such operations are costly and should be used only rarely. Yet in many problems, the size of a collection may be difficult to predict in advance, or may vary widely during the course of execution. For cases that suggest an alternative data structure, we examine the <B><I><A HREF="../stdlibref/list.html">list</A></I></B> datatype in this chapter. </P>
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<P>A <B><I><A HREF="../stdlibref/list.html">list</A></I></B> corresponds to the intuitive idea of holding elements in a linear sequence that is not necessarily ordered. New values can be added to or removed from either the front or the back of the <B><I>list</I></B>. By using an iterator to denote a position, elements can also be added to or removed from the middle of a <B><I>list</I></B>. In all cases the insertion or removal operations are efficient; they are performed in a constant amount of time that is independent of the number of elements being maintained in the collection. </P>
<P>A <B><I><A HREF="../stdlibref/list.html">list</A></I></B> is a linear structure. In general, elements of a <B><I>list</I></B> can only be accessed by a linear traversal of all values, not by subscript. </P>
<A NAME="611"><H3>6.1.1 Include files</H3></A>
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<P>Whenever you use a <B><I><A HREF="../stdlibref/list.html">list</A></I></B>, you must include the <SAMP>list</SAMP> header file:</P>

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#include &lt;list&gt;
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